I have to agree with Alexy. Let them bid and sell the job and pay you a flat commission on each job. Expecially in the KEC industry!
I've usually just told people to call someone I know and haven't bothered with the commission stuff because I haven't had the time or a system to keep track of it but I've been working on changing that.
Alexy has a good rep in this area, I've referred a few people to him this year. I don't know if I've ever met him or not but a few PW guys in the area told me about him.